A Philadelphia Highway Patrol officer remains in critical but stable condition following brain surgery after he was seriously injured when his motorcycle was hit by another vehicle in Northeast Philadelphia.

Doctors will be conducting minute-by-minute "aggressive monitoring" on 48-year-old Andy Chan to check on swelling on his brain, Philadelphia Police Commissioner Richard Ross said Friday morning.

Ross said there hasn't been much change to the officer's status, but "the next 72 hours are critical for Andy."

"It's good news in the sense that there's not a lot of change. Because of the significant injury that he sustained, that's actually a good sign right now," Ross said.

Chan's wife and son are with him in the Jefferson Torresdale Hospital, where the 24-year veteran of the force was transported with a large police escort after the crash. He was then taken into the operating room for brain surgery.

Chopper 6 over procession to hospital for injured motorcycle officer in Northeast Philadelphia on January 3, 2019.

"I cannot say enough about the trauma centers in this city. They are all stellar. What this one in particular did last night for one of our officers is nothing short of spectacular," Ross said.

Members of the highway patrol also remain at the hospital to support Chan; some, Ross said, may have been there most of the night.

Ross said there were upwards of 150 police officers who held vigil outside the hospital Thursday night. He said they are so loyal to their injured companion, some had to be encouraged to go home and get some rest.

The accident occurred along a section of Rhawn Street that runs between Roosevelt Boulevard and Frankford Avenue just after 5:30 p.m. Thursday.

Police said the 79-year-old driver of a Ford minivan was coming out of Pennypack Park on to Rhawn Street when he crashed into Officer Chan's motorcycle.

Investigators said the impact threw Chan about 25 feet.

Ross said he believes, as do the surgeons, that Chan's helmet helped him stay alive.

"We're just ever so hopeful that he is going to survive his injury and this traumatic ordeal and someday he will join us again, be able to don that uniform, and make us proud like he always has," Ross said.

The driver of the minivan remained at the scene of the accident. Ross said the driver was not impaired and there was no sign of recklessness.

"There's no indication this was nothing more than an accident. A 79-year-old male who apparently didn't see him when he was coming out of the park driveway. It's just tragic all around," Ross said. "I don't know the individual, but I can only imagine he knows what happened. He's got to deal with that. He's suffering over that, if he's any kind of decent human being. I like to believe most are. Again, I didn't speak to him."

Resident Robert Parisi was just getting home from work and he ran out to see what happened.

"I didn't even get in the door and I heard the police sirens coming," he said. "I didn't recognize it as a police motorcycle at first. It was a twisted wreck and it was in pieces."

Ross said although Chan was headed to his headquarters, he was on his marked cycle, so he would consider him on-duty.

Chan was very active in police recruiting. He was recently featured in a police recruiting video where he recalled as a boy the police officers who came into his parent's restaurant at 10th and Race streets to get something to eat.

"I said to them, 'I want to become a police officer,'" Chan says in the video.

He later would become a member of the department's elite Highway Patrol Unit. The highly decorated officer would also become a valuable advocate in the department's minority recruiting efforts.